ABSTRACT
In most gram-negative pathogens, and particularly in most wild-type members of the families Enterobacteriaceae, Pseudomonadaceae, Pasteurellaceae, and Vibrionaceae, the lipopolysaccharide (LPS) core is capped by an O-polysaccharide (O-PS) side chain to form smooth LPS (S-LPS). Structural diversity in the O-PSs defines the O-antigen specificity used in serological classifications. Much of the early interest in the chemistry, biosyn-thesis, and genetics of O-PSs originated from their roles as essential virulence determinants and their po7 tential application in the development of vaccines. The presence of O-PS at the periphery of the cell gives rise to a hydrophilic surface layer, which, based on location and structure, plays a critical role in the interactions between the bacterium and its environment. The chemistry, biosynthesis, and genetics of bacterial O-PSs has been most intensively studied in Salmonella and Escherichia coli. However, there is a growing body of information from comparative studies with other enteric organisms as well as from the Pseudomonadaceae and the Vibrionaceae.
